The present invention relates to a system for regulating the air supply conditions of a turboshaft machine.
The invention concerns in particular a regulation system for an air intake conduit system of a centrifugal compressor, and more particularly relates to an external centrifugal compressor of an auxiliary power unit employing a gas turbine drive.
The invention is more particularly applicable in the case of an annular conduit which is generally employed in turboshaft machines, and in particular in the intake part of the compressors, and which permits these machines to take in directly, or through a plenum, the surrounding air for suitably supplying air to their axial input part.
In the radial part of the gas intake conduit, means for regulating the air supply conditions of the turboshaft machine, such as directing vanes, are disposed around the axis of the machine and at even intervals on a given diameter. These vanes, arranged in the form of a ring, are generally of the design having a variable angular setting and they are simultaneously orientable between two extreme positions.
In one of these extreme setting positions, termed the completely open position, all the vanes are oriented substantially radially. In the other extreme setting position, termed the completely closed position, all the vanes are oriented tangentially relative to the annular gas inlet.
By modifying as required the angular setting of the vanes, it is possible to regulate with precision the air supply conditions of the compressor, and therefore to adapt the air flow and the pressure level delivered to the different circuits fed by this compressor.
In particular, and in the case of the completely closed position, the regulating system permits greatly reducing the air flow through the compressor and consequently the power required to drive it. Such an adaptation is required in the starting up stages of certain rotating machines having an external or auxiliary compressor.
In conventional adaptation devices of the type described hereinbefore, and for a given range of the angular setting of the vanes, the latter impose on the gas stream a gyratory flow in the direction toward the inlet of the compressor. This operation is desired to satisfy a certain incidence on the mobile blades of the compressor.
Under certain operating conditions, and in the case of the completely closed position for the vanes, an excessive heating may occur inside the compressor which results from an insufficient gas flow which heat then travels through the turboshaft machine. This heating may be harmful to the mechanical resistance and performance of the unit.
In order to overcome this drawback, it has already been proposed to construct means controlling the regulating system in which an actuating jack actuating the vanes provides a very small clearance between the vanes, in the closed position, so as to maintain a minimum gas flow through the compressor and avoid that the latter does not overheat. However, the resulting control means and the actuating jack are then of a complex and costly structure.
Further, upon the stopping of the turboshaft machine, the directing vanes are in the position of complete closure or substantially complete closure, and it is necessary to disassemble a part of the air intake device to effect an endoscopic inspection of certain elements of the auxiliary power unit, for example of the blades and vanes of the compressor. This inspection also necessitates being in a position, when the turboshaft machine stops, to control the regulating system so as to bring the vanes to their position termed the completely open position.